Carbon fiber reinforced plastic (CFRP) is superior in terms of specific rigidity, specific strength, fatigue property, and corrosive property compared with metal, and is examined to be applied to structural members of automobiles or the like for the sake of weight reduction.
However, there is no method of joining in a short time with ease like spot welding for the metal. This is one of factors to frustrate the weight reduction due to the material substitution.
In this regard, adhesive joining is generally used to join laminated plate materials made of CFRP.
However, there are problems such that an adhesive requires a long time to be hardened in view of productivity in the automobile industry, and joining surfaces require to be processed and cleaned to result in high cost.
Further, there is a problem in heat resistance, influence of moisture absorbent, weakness under cool environment or fast deformation, and the like.
On the other hand, as mechanical joining, rivet joining is used.
However, there are problems such that it requires a long time for a hole making process, and a tool becomes worn early compared with that for metal or the like.
From such a situation, a joining method capable of being carried out in a short time at low cost is highly demanded.
As a conventional joining method in this kind, there is one described in Patent Document 1.
This joining method of Patent Document 3 uses a self-piercing rivet (SPR) that has a rivet head and a hollow rivet body opened at a front end face, to fasten two FRP plates laid one on another.
Namely, a metal plate is brought into firmly contact with a portion of one FRP plate to be fastened, and then the self-piercing rivet (SPR) is driven into both the FRP plates from a portion of the other FRP plate to be fastened so that the rivet head is brought into firmly contact with the portion of the other FRP plate to be fastened. Further, an annular front end of the rivet body that pierces both the FRP plates is put to biting the metal plate and radially expanding. In this way, the FRP plates are joined together between the rivet head and the metal plate.
However, the method drives the rivet body into the metal plate and plastically deforms the metal plate, so that the FRP plates may be separated from each other and get cracked around the rivet body according to the plastic deformation. Therefore, this method has little or no readability and Patent Document 1 has been deemed to be withdrawn.
Further, not only when joining the FRP plates but also when joining thin metal plates or the like, separation may be caused between joining surfaces by driving the rivet body. This is the broadly possible problem in joining laminated plate materials, thin plate materials, or the like by driving a rivet.
Additionally, the joining by driving a rivet may perform spin crimping other than use of the SPR. That is not necessarily possible problem in only the SPR and is the broadly possible problem in joining by driving a rivet.